Wireless communication has grown to encompass a huge variety of information transactions between electronic machines. These include cellular communications between hand-held units and base stations, wireless communications between peer devices or client-server devices. To enhance the performance of wireless communication systems, multiple input multiple output (MIMO) wireless communication systems can include a plurality of radios at the transmitting or receiving devices of a two-way wireless communication system. Previously, a MIMO station or access point (AP) could only communicate with one device at time on a given frequency channel. Recently, multi user MIMO systems (MU-MIMO) have been developed to further advance the wireless communication capabilities to support simultaneous communication in the same frequency channel with a plurality of devices. FIG. 1 illustrates an MU-MIMO test system featuring a wireless AP 100 coupled over Ethernet 105 to a computer 120 handling transmit and receive data related to communications over the air (OTA) among several MU-MIMO stations 121-123 via AP 100. AP 100 and all three MU-MIMO stations 121-123 can implement the MU-MIMO mechanism according to, for example, 802.11ac or 802.11ax.
Testing wireless devices in an uncontrolled open air RF environment, such as the one presented in FIG. 1, is difficult due to uncontrolled interference and random reflections. MU-MIMO OTA testing is highly challenging because it requires repeatable conditions and specific device positioning in order to achieve repeatable and reliable results.
Shortcomings of controlled test systems include that they generally are carried out in a “conducted” test fashion, where the antenna of the device under test is removed and an RF cable connected directly to the antenna port of the radio. While this improves repeatability, conducted testing is unsuitable for measuring MU-MIMO gain, since antenna elements are involved in the MU-MIMO beamforming techniques and must be part of the test.
Therefore, for testing MU-MIMO performance, a better test environment and method are desired.